The oil and intake air filters commonly encountered in conjunction with internal combustion engines are exemplary of the filtering art and its associated problems. These filters utilize a somewhat porous paper filter element or similar filter media on which any undesirable particles are retained as fluid is passed through such filter element or media. As filtering continues, the filter element or media becomes more and more blocked by the removed particles which results in a further reduction of the flow rate even though the particle removing efficiency increases. These filtering systems essentially rely on adsorption which is a surface phenomenon wherein the removed particles adhere to the surface of the filter element or media. Another example of an adsorptive particle removal technique, is the use activated charcoal or a zeolite material as an odor removing element or media to purify an air stream. However, such techniques or method of purifying an air stream are effective only for a relative short time period, are relatively inefficient at low odor concentration levels, and frequently result in a relatively high pressure differential across the element or media. As a result very large quantity of media is the only satisfactory way in which to use these materials however the relative large pressure differential problem would remain.
A costly and complex solution to the flow rate and efficiency problems can be provided by employing absorption techniques wherein a counterflowing liquid and gas are intermingled in gas absorption tower with certain gas components being absorbed and removed by the liquid. Such "scrubbing " techniques are not suited to small solid filter applications since the interstices within the filter elements must be relatively large to avoid the liquid from clogging the filter elements and severely reducing air flow therethrough. These large openings significantly reduce the filtering efficiency.
An illustrative hybrid between the first two methods is shown in U.S. Pat. No. 4,323,373 which teaches an air cleaning system for a restaurant cooking grill wherein air is passed through filter elements which remove the undesirable materials and a scrubbing solution of water and detergent continuously circulates over the filter elements to remove congealed grease and other pollutants from those filter elements. Here, the filtering of particles from the air is an adsorption process, but the subsequent removal of the materials from the filter elements is an absorption process. This type system is relatively large and is adapted to high volume flow of relatively dirty air. While aptly suited to cooking grills, it is not well suited to more generalized odor removal functions. Also, as with the "scrubbers" mentioned above, the interstices within the filter elements must be relatively large to avoid the liquid from clogging the filter elements and severely reducing air flow therethrough.
It is desirable to provide a compact, economical absorptive air filter for the removal of odors which avoids the problems of reduced flow rates and reduced particle removing efficiency.
U.S. Pat. No. 5,057,368 entitled FILAMENTS HAVING TRILOBAL OR QUADRILOBAL CROSS-SECTIONS discloses a trilobal or quadrilobal fiber formed from thermoplastic polymers wherein the fiber has a cross-section comprised of a central core and three or four T-shaped lobes. The legs of each of the lobes intersect at the center of the core so that the angle between the legs of adjacent lobes is from about 80 to 130 degrees. The thermoplastic polymer is typically a nylon, a polyester, a polyolefin or a combination thereof. For example, a combination of a polyester such as polyethylene terephthalate and a polyolefin such as polypropylene may be used.